As is well known, as work vehicles used in civil engineering work and agricultural work of various types, there may be given one broadly put into practical use, which has a structure with which, with use of a hydraulic actuator constituted by a piston cylinder, an oil motor, and the like, an operation such as up-down movement is performed with respect to an operating member attached to a vehicle body. Examples of the work vehicle include well-known one adopting a structure in which a front loader having a bucket at a leading end thereof is detachably mounted to a vehicle body constituted by a tractor so that various operations are performed with the bucket while the leading end of the front loader is moved up-down with the hydraulic actuator.
In the work vehicles of this type, the hydraulic controller for controlling an operation of the actuator is provided with a spool valve as a direction switch valve. When the spool valve is used, oil leakage occurs from between the spool valve and a spool insertion hole because the spool valve is inserted into the spool insertion hole formed in a housing and is moved while sliding in a valve shaft direction. Thus, in the above-mentioned example, there is a disadvantage as follows: when the leading end of the front loader is stopped at a predetermined height position and left as it is in a state where an engine is turned off, the actuator is incapable of supporting the weight of the front loader owing to the oil leakage, with the result that the leading end of the front loader descends so that a posture of the bucket is disturbed.
In view of the problems as described above, for example, Patent Document 1 described below discloses a hydraulic controller in which a housing is provided with a switch-spool insertion hole through which a switch-spool valve as a direction switch valve is inserted, the switch-spool insertion hole being provided with a pair of ports to which a pair of supply/drain pipes continuous with an actuator are connected, and check valves for preventing communication of oil returning from the actuator toward the switch-spool insertion hole are provided to those ports, respectively. On the switch-spool valve of this controller, there are partially formed tapered surfaces at two points, each of which is gradually increased in diameter toward one side in the valve shaft direction. Leading ends of the check valves are arranged so as to be brought into contact with those tapered surfaces, respectively. In this context, when the switch-spool valve is moved from a neutral position into a valve shaft direction by manipulation, an electromagnetic means, or the like, the check valve provided in the port on a side from which pressure oil flows out into the actuator is opened by being pushed up by the pressure oil, and the check valve provided in the port on a side to which the pressure oil flows in from the actuator is opened by being pushed up by the tapered surface of the switch-spool valve.    Patent Document 1: JP 3839633 B